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Miller" , Jakub Kicinski , Simon Horman , Matthieu Baerts , Mat Martineau , Geliang Tang , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Shuah Khan , Florian Westphal , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH net v2 2/3] bpf,sockmap: disallow MPTCP sockets from sockmap updates In-Reply-To: <20251020060503.325369-3-jiayuan.chen@linux.dev> (Jiayuan Chen's message of "Mon, 20 Oct 2025 14:04:47 +0800") References: <20251020060503.325369-1-jiayuan.chen@linux.dev> <20251020060503.325369-3-jiayuan.chen@linux.dev> Date: Tue, 21 Oct 2025 12:49:19 +0200 Message-ID: <87cy6gwmvk.fsf@cloudflare.com> Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Mon, Oct 20, 2025 at 02:04 PM +08, Jiayuan Chen wrote: > MPTCP creates subflows for data transmission, and these sockets should not > be added to sockmap because MPTCP sets specialized data_ready handlers > that would be overridden by sockmap. > > Additionally, for the parent socket of MPTCP subflows (plain TCP socket), > MPTCP sk requires specific protocol handling that conflicts with sockmap's > operation(mptcp_prot). > > This patch adds proper checks to reject MPTCP subflows and their parent > sockets from being added to sockmap, while preserving compatibility with > reuseport functionality for listening MPTCP sockets. > > Fixes: 0b4f33def7bb ("mptcp: fix tcp fallback crash") > Signed-off-by: Jiayuan Chen > --- > net/core/sock_map.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/net/core/sock_map.c b/net/core/sock_map.c > index 5947b38e4f8b..da21deb970b3 100644 > --- a/net/core/sock_map.c > +++ b/net/core/sock_map.c > @@ -535,6 +535,15 @@ static bool sock_map_redirect_allowed(const struct sock *sk) > > static bool sock_map_sk_is_suitable(const struct sock *sk) > { > + if ((sk_is_tcp(sk) && sk_is_mptcp(sk)) /* subflow */ || > + (sk->sk_protocol == IPPROTO_MPTCP && sk->sk_state != TCP_LISTEN)) { > + /* Disallow MPTCP subflows and their parent socket. > + * However, a TCP_LISTEN MPTCP socket is permitted because > + * sockmap can also serve for reuseport socket selection. > + */ > + pr_err_once("sockmap: MPTCP sockets are not supported\n"); > + return false; > + } > return !!sk->sk_prot->psock_update_sk_prot; > } You're checking sk_state without sk_lock held. That doesn't seem right. Take a look how we always call sock_map_sk_state_allowed() after grabbing the lock. Same might apply to sk_is_mptcp(). Please double check.